Eccentricity correction method, signal processing circuit, magnetic storage apparatus and perpendicular magnetic recording medium

ABSTRACT

A magnetic storage apparatus has a reproducing head to reproduce information from a perpendicular magnetic recording medium that is recorded with servo information, eccentricity correction data and read/write data. The apparatus further has a filter part to filter a reproduced output of the reproducing head by filtering the servo information which has a differentiated waveform by a non-differentiating characteristic and by filtering the eccentricity correction data and the read/write data which have rectangular waveforms by a differentiating characteristic, a demodulating part to demodulate the servo information, the eccentricity correction data and the read/write data that are filtered by the filter part, and a servo system to carry out a control process including an eccentricity control based on the servo information and the eccentricity correction data that are demodulated.

This application is a Divisional of application Ser. No. 11/474,156,filed Jun. 23, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to eccentricity correctionmethods, signal processing circuits, magnetic storage apparatuses andperpendicular magnetic recording media, and more particularly to aneccentricity correction method for correcting eccentricity byreproducing an eccentricity correction data that is recorded by arecoding head from a perpendicular magnetic recording medium that isprerecorded with servo information by a magnetic transfer, a signalprocessing circuit and a magnetic storage apparatus that employ such aneccentricity correction method, and a perpendicular magnetic recordingmedium that is recorded with an eccentricity correction data in aneasily reproducible manner.

2. Description of the Related Art

A magnetic disk is prerecorded with servo information for controlling aposition of a head with respect to the magnetic disk. The servoinformation may be recorded by a recording head or, by a magnetictransfer that applies magnetization in an in-plane direction or aperpendicular direction with respect to the magnetic disk. The magnetictransfer itself is known, as may be seen from a Japanese Laid-OpenPatent Application No. 2004-342297.

After the magnetic disk that is prerecorded with the servo informationis assembled into a magnetic disk drive, an eccentricity correction datafor correcting eccentricity of the magnetic disk is recorded on themagnetic disk by a recording head. The eccentricity correction iscarried out in real-time by reproducing the eccentricity correction datafrom the magnetic disk by a reproducing head.

FIG. 1 is a system block diagram showing an important part of aconventional magnetic disk drive. A magnetic disk drive 1 shown in FIG.1 includes a preamplifier part 2, a read and write part 3, a hard diskcontroller (HDD) 4, and a servo controller (SVC) 5. The preamplifierpart 2 includes an amplifier 21 and a driver 22. The read and write part3 includes a synchronizing circuit 31, a prefilter 32, a switchingcircuit 33, a data demodulating circuit 34, a servo demodulating circuit35, a post processor 36, a recording compensation circuit 37, and adriver 38.

FIG. 2 is a diagram showing a format on a conventional perpendicularmagnetic disk. The perpendicular magnetic disk is provided with a servoregion in which servo information is prerecorded by a recording head.Data are recorded in a data region which follows the servo region. Apreamble #1, servo mark and address, and servo burst are prerecorded inthe servo region. After the perpendicular magnetic disk is assembledinto the magnetic disk drive 1, an eccentricity correction data isrecorded in the servo region by the recording head subsequent to theservo burst. At the time of a recording, the data is recorded subsequentto a preamble #2. At the time of a reproduction, the recorded data isreproduced from the data region. The data that are reproduced andrecorded with respect to the data region are shown as R/W (read/write)data in FIG. 2.

Information reproduced from the perpendicular magnetic disk (not shown)by the reproducing head (not shown) is supplied to the data demodulatingcircuit 34 and the servo demodulating circuit 35 via the amplifier 21,the synchronizing circuit 31 and the prefilter 32. The synchronizingcircuit 31 generates a clock and a servo mark from the reproducedinformation, and supplies the clock and the servo mark to the switchingcircuit 33. The switching circuit 33 controls switching of thedemodulating circuits 34 and 35 based on the clock and the servo mark,so that the output of the prefilter 32 is demodulated by the servodemodulating circuit 35 while reproducing the information from the servoregion and the output of the prefilter 32 is demodulated by the datademodulating circuit 34 while reproducing the information from the dataregion. Output reproduced data from the data demodulating circuit 34 aresupplied to the HDC 4, and output reproduced servo information from theservo demodulating circuit 35 is supplied to the SVC 5. The reproduceddata are supplied to other parts within the magnetic disk drive 1 or,output outside the magnetic disk drive 1, via the HDC 4. The reproducedservo information is used for various kinds of control operations of themagnetic disk drive 1 in the SVC 5.

At the time of the recording, the recording data are supplied to therecording head (not shown) via the HDC 4, the post processor 36, therecording compensation circuit 37 and the drivers 38 and 22. Hence therecording head records the recording data within the data region on theperpendicular magnetic disk subsequent to the preamble #2.

According to the format shown in FIG. 2, both the information within theservo region and the information within the data region that arereproduced by the reproducing head are reproduced in the form of arectangular wave. Hence, the prefilter 32 has a differentiatingcharacteristic.

However, the method of recording the servo information on the magneticdisk by the magnetic transfer is more efficient that the method ofrecording the servo information by the recording head, in that the servoinformation can be recorded simultaneously, that is, in a batch. Inaddition, in the case of the magnetic transfer that applies themagnetization in the in-plane direction with respect to theperpendicular magnetic disk, it is further desirable in that thesignal-to-noise ratio (SNR) improves. FIG. 3 is a diagram showing aformat on a perpendicular magnetic disk that is recorded with the servoinformation by the magnetic transfer which applies the magnetization inthe in-plane direction with respect to the perpendicular magnetic disk,and is also recorded with the eccentricity correction data by therecording head.

But in the case of the perpendicular magnetic disk that is recorded withthe servo information by the magnetic transfer which applies themagnetization in the in-plane direction with respect to theperpendicular magnetic disk and is recorded with the eccentricitycorrection data by the recording head, the preamble #1, the servo markand address, and the servo burst that are reproduced by the reproducinghead are reproduced in the form of differentiated waveforms and cannotbe subjected to the same process as the eccentricity correction datawithin the servo region and the information within the data region thatare reproduced in the form of rectangular waveforms. In other words, ifthe prefilter 32 has a differentiating characteristic, this prefilter 32will not be suited for processing the preamble #1, the servo mark andaddress, and the servo burst within the servo region that are reproducedin the form of differentiated waveforms, and cannot carry out a suitableprefiltering with respect to the servo information that is to besupplied to the servo demodulating circuit 35. On the other hand if theprefilter 32 has a non-differentiating characteristic, this prefilter 32will not be suited for processing the eccentricity correction datawithin the servo region and the information within the data region thatare reproduced in the form of rectangular waveforms, and cannot carryout a suitable prefiltering with respect to the eccentricity correctiondata to be supplied to the servo demodulating circuit 35 and the data tobe supplied to the data demodulating circuit 34.

For this reason, in the case of the perpendicular magnetic recordingmedium that is prerecorded with the servo information by the magnetictransfer which applies the magnetization in the in-plane direction withrespect to the perpendicular magnetic recording medium, there was aproblem in that the eccentricity correction cannot be made byreproducing the eccentricity correction data that has been recorded bythe recording head.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful eccentricity correction method, signal processingcircuit, magnetic storage apparatus and perpendicular magnetic recordingmedium, in which the problems described above are suppressed.

Another and more specific object of the present invention is to providean eccentricity correction method, a signal processing circuit, amagnetic storage apparatus and a perpendicular magnetic recordingmedium, which can carry out an eccentricity correction by reproducing aneccentricity correction data that has been recorded by a recording headfrom a perpendicular magnetic recording medium that is prerecorded withservo information by a magnetic transfer which applies a magnetizationin an in-plane direction with respect to the perpendicular magneticrecording medium.

Still another object of the present invention is to provide aneccentricity correction method comprising a reproducing step reproducinginformation from a perpendicular magnetic recording medium that isrecorded with servo information, eccentricity correction data andread/write data, by a reproducing head; a filtering step filtering areproduced output of the reproducing head, by filtering the servoinformation which has a differentiated waveform by a non-differentiatingfilter characteristic, and by filtering the eccentricity correction dataand the read/write data which have rectangular waveforms by adifferentiating filter characteristic; a demodulating step demodulatingthe servo information, the eccentricity correction data and theread/write data that are filtered by the filtering step; and an outputstep outputting the demodulated servo information and eccentricitycorrection data to a servo system which carries out a control processincluding an eccentricity correction, and the demodulated read/writedata to a data processing system. According to the eccentricitycorrection method of the present invention, it is possible to carry outan eccentricity correction by reproducing the eccentricity correctiondata that has been recorded by the recording head from the perpendicularmagnetic recording medium that is prerecorded with the servo informationby the magnetic transfer which applies the magnetization in the in-planedirection with respect to the perpendicular magnetic recording medium.

A further object of the present invention is to provide a magneticstorage apparatus comprising a reproducing head configured to reproduceinformation from a perpendicular magnetic recording medium that isrecorded with servo information, eccentricity correction data andread/write data; a filter part configured to filter a reproduced outputof the reproducing head, by filtering the servo information which has adifferentiated waveform by a non-differentiating filter characteristic,and by filtering the eccentricity correction data and the read/writedata which have rectangular waveforms by a differentiating filtercharacteristic; a demodulating part configured to demodulate the servoinformation, the eccentricity correction data and the read/write datathat are filtered by the filter part; a servo system configured to carryout a control process including an eccentricity control based on theservo information and the eccentricity correction data that aredemodulated; and a data processing system configured to process theread/write data that are demodulated. According to the magnetic storageapparatus of the present invention, it is possible to carry out aneccentricity correction by reproducing the eccentricity correction datathat has been recorded by the recording head from the perpendicularmagnetic recording medium that is prerecorded with the servo informationby the magnetic transfer which applies the magnetization in the in-planedirection with respect to the perpendicular magnetic recording medium.

Another object of the present invention is to provide a perpendicularmagnetic recording medium which is prerecorded with servo informationfor controlling a position of a head with respect to the perpendicularmagnetic recording medium, by a magnetic transfer that applies amagnetization in an in-plane direction with respect to the perpendicularmagnetic recording medium, comprising a servo region recorded with afirst preamble, the servo information, a second preamble and aneccentricity correction data; and a data region recorded with a thirdpreamble and read/write data, wherein the first, second and thirdpreambles are made up of patterns having a constant period and mutuallydifferent frequencies, and the second preamble, the eccentricitycorrection data, the third preamble and the read/write data are recordedby a recording head. According to the perpendicular magnetic recordingmedium of the present invention, it is possible to carry out aneccentricity correction by reproducing the eccentricity correction datathat has been recorded by the recording head from the perpendicularmagnetic recording medium that is prerecorded with the servo informationby the magnetic transfer which applies the magnetization in the in-planedirection with respect to the perpendicular magnetic recording medium.

Still another object of the present invention is to provide aperpendicular magnetic recording medium which is prerecorded with servoinformation for controlling a position of a head with respect to theperpendicular magnetic recording medium, by a magnetic transfer thatapplies a magnetization in an in-plane direction with respect to theperpendicular magnetic recording medium, comprising a servo regionrecorded with a first preamble and the servo information; and a dataregion recorded with a second preamble, an eccentricity correction dataand read/write data, wherein the first and second preambles are made upof patterns having a constant period and mutually different frequencies,and the second preamble, the eccentricity correction data, the thirdpreamble and the read/write data are recorded by a recording head.According to the perpendicular magnetic recording medium of the presentinvention, it is possible to carry out an eccentricity correction byreproducing the eccentricity correction data that has been recorded bythe recording head from the perpendicular magnetic recording medium thatis prerecorded with the servo information by the magnetic transfer whichapplies the magnetization in the in-plane direction with respect to theperpendicular magnetic recording medium.

A further object of the present invention is to provide a signalprocessing circuit comprising a filter part configured to filter areproduced output of a reproducing head, by filtering servo informationwhich has a differentiated waveform by a non-differentiating filtercharacteristic, and by filtering an eccentricity correction data andread/write data which have rectangular waveforms by a differentiatingfilter characteristic; a demodulating part configured to demodulate theservo information, the eccentricity correction data and the read/writedata that are filtered by the filter part; a servo system configured tocarry out a control process including an eccentricity control based onthe servo information and the eccentricity correction data that aredemodulated; and a data processing system configured to process theread/write data that are demodulated. According to the signal processingcircuit of the present invention, it is possible to carry out aneccentricity correction by reproducing the eccentricity correction datathat has been recorded by the recording head from the recording mediumthat is prerecorded with the servo information by the magnetic transferwhich applies the magnetization in the in-plane direction with respectto the perpendicular magnetic recording medium.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system block diagram showing an important part of aconventional magnetic disk drive;

FIG. 2 is a diagram showing a format on a conventional perpendicularmagnetic disk;

FIG. 3 is a diagram showing a format on a perpendicular magnetic diskthat is recorded with servo information by a magnetic transfer thatapplies magnetization in an in-plane direction with respect to theperpendicular magnetic disk;

FIG. 4 is a system block diagram showing a first embodiment of amagnetic storage apparatus according to the present invention;

FIG. 5 is a diagram showing a format of a first embodiment of aperpendicular magnetic recording medium according to the presentinvention;

FIG. 6 is a plan view showing the format shown in FIG. 5;

FIG. 7 is a diagram for explaining an output of a reproducing head;

FIG. 8 is a system block diagram showing a second embodiment of themagnetic storage apparatus according to the present invention;

FIG. 9 is a system block diagram showing a third embodiment of themagnetic storage apparatus according to the present invention;

FIG. 10 is a diagram showing a format of a third embodiment of theperpendicular magnetic recording medium according to the presentinvention;

FIG. 11 is a plan view showing the format shown in FIG. 10;

FIG. 12 is a system block diagram showing a fourth embodiment of themagnetic storage apparatus according to the present invention; and

FIG. 13 is a system block diagram showing a fifth embodiment of themagnetic storage apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given of various embodiments of the eccentricitycorrection method, the signal processing circuit, the magnetic storageapparatus and the perpendicular magnetic recording medium according tothe present invention, by referring to FIG. 4 and the subsequentdrawings.

First Embodiment

FIG. 4 is a system block diagram showing a first embodiment of themagnetic storage apparatus according to the present invention. Thisfirst embodiment of the magnetic storage apparatus employs a firstembodiment of the signal processing circuit according to the presentinvention, a first embodiment of the eccentricity correction methodaccording to the present invention, and a first embodiment of theperpendicular magnetic recording medium (having a format shown in FIG.5) according to the present invention.

A magnetic disk drive 41-1 shown in FIG. 4 includes a reproducing head40R, a recording head 40W, a preamplifier part 42, a read and write part43-1, a hard disk controller (HDC) 44, and a servo controller (SVC) 45.The preamplifier part 42 includes an amplifier 421 and a driver 422. Theread and write part 43-1 includes a synchronizing circuit 431-1, aprefilter part 432-1, switching circuits 433-1 and 434-1, a datademodulating circuit 435, a servo demodulating circuit 436, a postprocessor 437, a recording compensation circuit 438, and a driver 439.The prefilter part 432-1 includes a prefilter 51 having anon-differentiating characteristic, and a prefilter 52 having adifferentiating characteristic. In this embodiment, each of theprefilters 51 and 52 is made up of a finite impulse response (FIR)filter. The signal processing circuit includes at least the prefilterpart 432-1, the data demodulating circuit 435, the servo demodulatingcircuit 436, the HDC 44 and the SVC 45.

FIG. 5 is a diagram showing a format of the first embodiment of theperpendicular magnetic recording medium according to the presentinvention. A perpendicular magnetic disk 500-1 has a servo region and adata region which follows the servo region. A servo mark and address,and a servo burst are prerecorded subsequent to a preamble P1 within theservo region by a known magnetic transfer which applies a magnetizationin an in-plane direction of the perpendicular magnetic disk 500-1. Theperpendicular magnetic disk 500-1 after the magnetic transfer isassembled into the magnetic disk drive 41-1, and an eccentricitycorrection data (or a post code) is recorded within the servo region bythe recording head 40W subsequent to the a preamble P2 following theservo burst within the servo region. The preamble P1 is made up ofpatterns having a constant period and is recorded for use in controllingread timings of the servo mark and address, and the servo burst. Thepreamble P2 is made up of patterns having a constant period and isrecorded for use in controlling a read timing of the eccentricitycorrection data. The eccentricity correction data itself is a correctiondata that is used to carry out a known eccentricity correction, that is,a repeatable run out (RRO) correction in real-time, and is obtainable bya known method. Data are recorded subsequent to a preamble P3 within thedata region which follows the servo region. In the data region, the dataare recorded by the recording head 40W subsequent to the preamble P3 atthe time of the recording, and the recorded data are reproduced by thereproducing head 40R at the time of the reproduction. The data that arereproduced and recorded with respect to the data region are shown as R/W(read/write) data in FIG. 5. The preamble P3 is made up of patternshaving a constant period and is recorded for use in controlling a readtiming of the R/W data. Since patterns of the preambles P1, P2 and P3have mutually different frequencies, it is possible to easilydistinguish the information following each of the preambles P1, P2 andP3.

FIG. 6 is a plan view showing the format shown in FIG. 5. For example,an upward direction in FIG. 6 corresponds to an inner peripheraldirection of the perpendicular magnetic disk 500-1, and a downwarddirection in FIG. 6 corresponds to an outer peripheral direction of theperpendicular magnetic disk 500-1. In addition, one-dot chain lines inFIG. 6 indicate centerlines of two mutually adjacent tracks. The tracksare formed concentrically or, as track turns of a spiral track, on theperpendicular magnetic disk 500-1.

FIG. 7 is a diagram for explaining an output of the reproducing head40R. As shown in FIG. 7, the reproducing head 40R outputs differentiatedwaveforms when reproducing the preamble P1, the servo mark and address,and the servo burst within the servo region that are recorded by themagnetic transfer. In addition, the reproducing head 40R outputsrectangular waveforms when reproducing the preamble P2 and theeccentricity correction data within the servo region that are recordedby the recording head 40W. Furthermore, the reproducing head 40R outputsrectangular waveforms when reproducing the preamble P3 and the R/W datawithin the data region that are recorded by the recording head 40W. Theservo information frequency (including the eccentricity correction data)within the servo region is constant for the entire region on theperpendicular magnetic disk 500-1. On the other hand, the R/W datafrequency within the data region is different for each zone (or region)that is formed in a ring-shape in a radial direction of theperpendicular magnetic disk 500-1.

The information that is reproduced from the perpendicular magnetic disk500-1 by the reproducing head 40R is supplied to the data demodulatingcircuit 435 and the servo demodulating circuit 436 via the amplifier421, the synchronizing circuit 431-1 and the prefilter part 432-1. Thesynchronizing circuit 431-1 generates clocks CK1 through CK3 and theservo mark from the reproduced information, supplies the clocks CK1 andCK2 (or the clocks CK1 and CK3) and the servo mark to the switchingcircuit 433-1, and supplies the clocks CK2 and CK3 (or only the clockCK2) and the servo mark to the switching circuit 434-1. Moreover, thesynchronizing circuit 431-1 supplies the clocks CK1 and CK2 to the servodemodulating circuit 436, and supplies the clock CK3 to the datademodulating circuit 435.

For example, the synchronizing circuit 431-1 generates from the patternsof the preamble P1 a clock CK1 having twice the fundamental frequencythereof, generates from the patterns of the preamble P2 a clock CK2having twice the fundamental frequency thereof, and generates from thepatterns of the preamble P3 a clock CK3 having twice the fundamentalfrequency thereof. The synchronizing circuit 431-1 reads the preamble P1and the servo mark and address and the servo burst immediately after thepreamble P1 within the servo region, in synchronism with the clock CK1,and reads the preamble P2 and the eccentricity correction data withinthe servo region in synchronism with the clock CK2. In addition, thesynchronizing circuit 431-1 reads the preamble P3 and the R/W datawithin the data region in synchronism with the clock CK3.

The switching circuit 433-1 controls the switching of the prefilter part432-1 so as to selectively output an output of the prefilter 51 whilereading the preamble P1, the servo mark and address, and the servo burstwithin the servo region, based on the clock CK1 and the servo mark, andto selectively output an output of the prefilter 52 while reading thepreamble P2 and the eccentricity correction data within the servo regionand the preamble P3 and the R/W data within the data region, based onthe clock CK2 and the servo mark. For example, a first switching signalthat is output from the switching circuit 433-1 to the prefilter part432-1 becomes active to switch the output of the prefilter part 432-1from the output of the prefilter 51 to the output of the prefilter 52 ata timing which is m1 periods after the servo mark by counting the clockCK1 using the servo mark as a trigger, and becomes inactive to switchthe output of the prefilter part 432-1 from the output of the prefilter52 to the output of the prefilter 51 at a timing which is m2 periodsafter the servo mark by counting the clock CK1 using the servo mark as atrigger.

In addition, the switching circuit 434-1 controls the switching of thedemodulating circuits 435 and 436 based on the clocks CK2 and CK3 (oronly the clock CK2) and the servo mark, so that the output of theprefilter part 432-1 is demodulated by the servo demodulating circuit436 while reading the servo region and the output of the prefilter part432-1 is demodulated by the data demodulating circuit 435 while readingthe data region. For example, a second switching signal that is outputfrom the switching circuit 434-1 to the demodulating circuits 435 and436 becomes active to make the data demodulating circuit 435 active (orto enable the data demodulating circuit 435) and the servo demodulatingcircuit 436 inactive (or to disable the servo demodulating circuit 436)at a timing which is n1 periods after the servo mark by counting theclock CK1 using the servo mark as a trigger, and becomes inactive tomake the data demodulating circuit 435 inactive and the servodemodulating circuit 436 active at a timing which is n2 periods afterthe servo mark by counting the clock CK1 using the servo mark as atrigger.

When active, the servo demodulating circuit 436 demodulates the preambleP1, the servo mark and address, and the servo burst within the servoregion in synchronism with the clock CK1, demodulates the preamble P2and the eccentricity correction data within the servo region insynchronism with the clock CK2, and supplies the demodulated servoinformation and the demodulated eccentricity correction data to the SVC45. The demodulated servo information and the demodulated eccentricitycorrection data are used for various kinds of control processes,including the eccentricity control process, in the SVC 45 which forms aservo system of the magnetic disk drive 41-1. When active, the datademodulating circuit 435 demodulates the preamble P3 and the R/W datawithin the data region in synchronism with the clock CK3, and suppliesthe demodulated R/W data to the HDC 44. The demodulated R/W data isoutput via the HDC 44 which forms a data processing system of themagnetic disk drive 41-1, to other parts within the magnetic disk drive41-1 or, to the outside of the magnetic disk drive 41-1.

At the time of the recording, the recording data is supplied to therecording head 40W via the HDC 44, the post processor 437, the recordingcompensation circuit 438 and the drivers 439 and 422. Hence, therecording data are recorded subsequent to the preamble P3 within thedata region of the perpendicular magnetic disk 500-1 by the recordinghead 40W.

According to this embodiment, the servo mark and address and the servoburst are prerecorded subsequent to the preamble P1 within the servoregion of the perpendicular magnetic disk 500-1 by the magnetic transferwhich applies the magnetization in the in-plane direction with respectto the perpendicular magnetic disk 500-1, while the eccentricitycorrection data within the servo region are recorded by the recordinghead 40W. However, it is possible to satisfactorily reproduce the servoinformation within the servo region that is recorded by differentrecording systems (or recording techniques). As a result, it is possibleto simultaneously improve the SNR by the magnetic transfer which appliesthe magnetization in the in-plane direction and carry out a satisfactoryeccentricity correction based on the eccentricity correction data.

Second Embodiment

FIG. 8 is a system block diagram showing a second embodiment of themagnetic storage apparatus according to the present invention. Thissecond embodiment of the magnetic storage apparatus employs a secondembodiment of the signal processing circuit according to the presentinvention, a second embodiment of the eccentricity correction methodaccording to the present invention, and a second embodiment of theperpendicular magnetic recording medium according to the presentinvention. The format of this second embodiment of the perpendicularmagnetic recording medium may be the same as the format of the firstembodiment shown in FIG. 5, and an illustration and description thereofwill be omitted. In FIG. 8, those parts that are the same as thosecorresponding parts in FIG. 4 are designated by the same referencenumerals, and a description thereof will be omitted. A signal processingcircuit includes at least a prefilter part 432-2, a data demodulatingcircuit 435, a servo demodulating circuit 436, an HDC 44 and a SVC 45.

As shown in FIG. 8, a magnetic disk drive 41-2 includes a read and writepart 43-2. The read and write part 43-2 has a prefilter part 432-2, andthe prefilter part 432-2 has a filter coefficient storage part 61 and aprefilter 62. The filter coefficient storage part 61 stores first filtercoefficients for operating the prefilter 62 as a FIR having anon-differentiating characteristic, and second filter coefficients foroperating the prefilter 62 as a FIR having a differentiatingcharacteristic. The first or second filter coefficients stored in thefilter coefficient storage part 61 are set in the prefilter 62 based onthe first switching signal from the switching circuit 433-1.

The switching circuit 433-1 controls the switching of the prefilter part432-2 so as to set the first filter coefficients in the prefilter 62while reading the preamble P1, the servo mark and address, and the servoburst within the servo region, based on the clock CK1 and the servomark, and to set the second filter coefficients in the prefilter 62while reading the preamble P2 and the eccentricity correction datawithin the servo region and the preamble P3 and the R/W data within thedata region, based on the clock CK2 and the servo mark. For example, thefirst switching signal that is output from the switching circuit 433-1to the prefilter part 432-2 becomes active to switch the filtercoefficients that are set in the prefilter 62 from the first filtercoefficients to the second filter coefficients at the timing which is m1periods after the servo mark by counting the clock CK1 using the servomark as a trigger, and becomes inactive to switch the filtercoefficients set in the prefilter 62 from the second filter coefficientsto the first filter coefficients at the timing which is m2 periods afterthe servo mark by counting the clock CK1 using the servo mark as atrigger. Hence, the output of the prefilter part 432-2 becomes the sameas the output of the prefilter part 432-1 of the first embodimentdescribed above.

According to this embodiment, it is possible to obtain effects similarto those obtainable in the first embodiment described above.

Third Embodiment

FIG. 9 is a system block diagram showing a third embodiment of themagnetic storage apparatus according to the present invention. Thisthird embodiment of the magnetic storage apparatus employs a thirdembodiment of the signal processing circuit according to the presentinvention, a third embodiment of the eccentricity correction methodaccording to the present invention, and a third embodiment of theperpendicular magnetic recording medium (having a format shown in FIG.10) according to the present invention. In FIG. 9, those parts that arethe same as those corresponding parts in FIG. 4 are designated by thesame reference numerals, and a description thereof will be omitted. Asignal processing circuit includes at least a prefilter part 432-1, adata demodulating circuit 435, a servo demodulating circuit 436, an HDC44 and a SVC 45.

As shown in FIG. 9, a magnetic disk drive 41-3 includes a read and writepart 43-3. The read and write part 43-3 has a synchronizing circuit431-2, switching circuits 433-2 and 434-2, a data demodulating circuit435, a servo demodulating circuit 436, and a selector circuit 441.

FIG. 10 is a diagram showing the format of the third embodiment of theperpendicular magnetic recording medium according to the presentinvention. A perpendicular magnetic disk 500-2 has a servo region and adata region which follows the servo region. A servo mark and address,and a servo burst are prerecorded subsequent to a preamble P1 within theservo region by a known magnetic transfer which applies a magnetizationin an in-plane direction of the perpendicular magnetic disk 500-2. Theperpendicular magnetic disk 500-2 after the magnetic transfer isassembled into the magnetic disk drive 41-3, and an eccentricitycorrection data (or a post code) is recorded within the data region bythe recording head 40W subsequent to the a preamble P4 following theservo burst within the servo region. The preamble P1 is made up ofpatterns having a constant period and is recorded for use in controllingread timings of the servo mark and address, and the servo burst. Thepreamble P4 is made up of patterns having a constant period and isrecorded for use in controlling read timings of the eccentricitycorrection data and the R/W data. The eccentricity correction dataitself is a correction data that is used to carry out a knowneccentricity correction, that is, an RRO correction in real-time, and isobtainable by a known method. Data are recorded in the data regionsubsequent to the eccentricity correction data within the data region.In the data region, the data are recorded by the recording head 40Wsubsequent to the eccentricity correction data at the time of therecording, and the recorded data are reproduced by the reproducing head40R at the time of the reproduction. The data that are reproduced andrecorded with respect to the data region are shown as R/W (read/write)data in FIG. 10. Since patterns of the preambles P1 and P4 have mutuallydifferent frequencies, it is possible to easily distinguish theinformation following each of the preambles P1 and P4.

In this case, the reproducing head 40R outputs differentiated waveformswhen reproducing the preamble P1, the servo mark and address, and theservo burst within the servo region that are recorded by the magnetictransfer. In addition, the reproducing head 40R outputs rectangularwaves when reproducing the preamble P4, the eccentricity data and theR/W data within the data region that are recorded by the recording head40W.

FIG. 11 is a plan view showing the format shown in FIG. 10. For example,an upward direction in FIG. 11 corresponds to an inner peripheraldirection of the perpendicular magnetic disk 500-2, and a downwarddirection in FIG. 11 corresponds to an outer peripheral direction of theperpendicular magnetic disk 500-2. In addition, one-dot chain lines inFIG. 11 indicate centerlines of two mutually adjacent tracks. The tracksare formed concentrically or, as track turns of a spiral track, on theperpendicular magnetic disk 500-2.

The R/W data frequency within the data region (including theeccentricity correction data) is different for each zone (or region)that is formed in a ring-shape in a radial direction of theperpendicular magnetic disk 500-2.

For example, the synchronizing circuit 431-2 generates from the patternsof the preamble P1 a clock CK1 having twice the fundamental frequencythereof, and generates from the patterns of the preamble P4 a clock CK4having twice the fundamental frequency thereof. The synchronizingcircuit 431-2 reads the preamble P1 and the servo mark and address andthe servo burst immediately after the preamble P1 within the servoregion, in synchronism with the clock CK1, and reads the preamble P4 andthe eccentricity correction data and the R/W data within the data regionin synchronism with the clock CK4.

The switching circuit 433-2 controls the switching of the prefilter part432-1 so as to selectively output an output of the prefilter 51 whilereading the preamble P1, the servo mark and address, and the servo burstwithin the servo region, based on the clock CK1 and the servo mark, andto selectively output an output of the prefilter 52 while reading thepreamble P4, the eccentricity correction data and the R/W data withinthe data region, based on the clock CK4 and the servo mark. For example,the first switching signal that is output from the switching circuit433-2 to the prefilter part 432-1 becomes active to switch the output ofthe prefilter part 432-1 from the output of the prefilter 51 to theoutput of the prefilter 52 at a timing which is m3 periods after theservo mark by counting the clock CK1 using the servo mark as a trigger,and becomes inactive to switch the output of the prefilter part 432-1from the output of the prefilter 52 to the output of the prefilter 51 ata timing which is m4 periods after the servo mark by counting the clockCK1 using the servo mark as a trigger.

In addition, the switching circuit 434-2 controls the switching of thedemodulating circuits 435 and 436 based on the clocks CK1 and CK4 andthe servo mark, so that the output of the prefilter part 432-1 isdemodulated by the servo demodulating circuit 436 while reading theservo region and the output of the prefilter part 432-1 is demodulatedby the data demodulating circuit 435 while reading the data region. Forexample, the second switching signal that is output from the switchingcircuit 434-2 to the demodulating circuits 435 and 436 becomes active tomake the data demodulating circuit 435 active (or to enable the datademodulating circuit 435) and the servo demodulating circuit 436inactive (or to disable the servo demodulating circuit 436) at a timingwhich is n3 periods after the servo mark by counting the clock CK1 usingthe servo mark as a trigger, and becomes inactive to make the datademodulating circuit 435 inactive and the servo demodulating circuit 436active at a timing which is n4 periods after the servo mark by countingthe clock CK1 using the servo mark as a trigger.

The output of the data demodulating circuit 435 is supplied to theselector circuit 441. For example, the selector circuit 441 selectivelyoutputs to the SVC 45 the output of the data demodulating circuit 435(that is, the eccentricity correction data) from a timing which is n3periods after the servo mark to a timing which is n5 periods after theservo mark by counting the clock CK1 using the servo mark from thesynchronizing circuit 431-2 as a trigger, and selectively outputs to theHDC 44 the output of the data demodulating circuit 435 (that is, the R/Wdata) from a timing which is n5 periods after the servo mark to a timingwhich is n4 periods after the servo mark. Hence, the demodulated R/Wdata from the data demodulating circuit 435 are supplied to the HDC 44,and the demodulated servo information (servo mark and address, and servoburst) from the servo demodulating circuit 436 and the demodulatedeccentricity correction data from the data demodulating circuit 435 aresupplied to the SVC 45.

According to this embodiment, it is possible to obtain effects similarto those obtainable in the first embodiment described above. Inaddition, since the common preamble P4 is used to identify theeccentricity correction data and the R/W data in the case of theperpendicular magnetic disk 500-2, it is possible to improve the formatefficiency compared to that of the perpendicular magnetic disk 500-1.

Fourth Embodiment

FIG. 12 is a system block diagram showing a fourth embodiment of themagnetic storage apparatus according to the present invention. Thisfourth embodiment of the magnetic storage apparatus employs a fourthembodiment of the signal processing circuit according to the presentinvention, a fourth embodiment of the eccentricity correction methodaccording to the present invention, and a fourth embodiment of theperpendicular magnetic recording medium according to the presentinvention. The format of this fourth embodiment of the perpendicularmagnetic recording medium may be the same as the format of the thirdembodiment shown in FIG. 10, and an illustration and description thereofwill be omitted. In FIG. 12, those parts that are the same as thosecorresponding parts in FIGS. 8 and 9 are designated by the samereference numerals, and a description thereof will be omitted. A signalprocessing circuit includes at least a prefilter part 432-2, a datademodulating circuit 435, a servo demodulating circuit 436, an HDC 44and a SVC 45.

The switching circuit 433-2 controls the switching of the prefilter part432-2 so as to set the first filter coefficients in the prefilter 62while reading the preamble P1, the servo mark and address, and the servoburst within the servo region, based on the clock CK1 and the servomark, and to set the second filter coefficients in the prefilter 62while reading the preamble P4, the eccentricity correction data and theR/W data within the data region, based on the clock CK4 and the servomark. For example, the first switching signal that is output from theswitching circuit 433-2 to the prefilter part 432-2 becomes active toswitch the filter coefficients that are set in the prefilter 62 from thefirst filter coefficients to the second filter coefficients at thetiming which is m3 periods after the servo mark by counting the clockCK1 using the servo mark as a trigger, and becomes inactive to switchthe filter coefficients set in the prefilter 62 from the second filtercoefficients to the first filter coefficients at the timing which is m4periods after the servo mark by counting the clock CK1 using the servomark as a trigger.

According to this embodiment, it is possible to obtain effects similarto those obtainable in the first embodiment described above. Inaddition, since the common preamble P4 is used to identify theeccentricity correction data and the R/W data in the case of theperpendicular magnetic disk 500-2, it is possible to improve the formatefficiency compared to that of the perpendicular magnetic disk 500-1.

Fifth Embodiment

FIG. 13 is a system block diagram showing a fifth embodiment of themagnetic storage apparatus according to the present invention. Thisfifth embodiment of the magnetic storage apparatus employs a fifthembodiment of the signal processing circuit according to the presentinvention, a fifth embodiment of the eccentricity correction methodaccording to the present invention, and a fifth embodiment of theperpendicular magnetic recording medium according to the presentinvention. The format of this fifth embodiment of the perpendicularmagnetic recording medium may be the same as the format of the firstembodiment shown in FIG. 5 or, the format of the third embodiment shownin FIG. 10, and an illustration and description thereof will be omitted.A signal processing circuit includes at least a prefilter part 432, adata demodulating circuit 435, a servo demodulating circuit 436, an HDC44 and a SVC 45.

FIG. 13 only shows an important part of the fifth embodiment of themagnetic storage apparatus. In FIG. 13, those parts that are the same asthose corresponding parts in FIG. 4 are designated by the same referencenumerals, and a description thereof will be omitted. As shown in FIG.13, in a read and write part 43-5 of a magnetic disk drive 41-5, theprefilter part 432 constantly supplies an output of a synchronizingcircuit 431 to a selector circuit 600 via prefilters 51A and 51B. Theprefilter 51A has a non-differentiating filter characteristic, and theprefilter 52A has a differentiating filter characteristic. The selectorcircuit 600 inputs one of outputs of the prefilters 51A and 52A at atiming based on the clocks CK1 through CK3 from the synchronizingcircuit 431, and selectively outputs the one of the outputs input to theselector circuit 600 to one of the data demodulating circuit 435 and theservo demodulating circuit 436.

In the case where the fifth embodiment of the perpendicular magneticrecording medium uses the same format as the first embodiment, theperpendicular magnetic disk 500-1 has the format shown in FIG. 5. Inthis case, the input of the selector circuit 600 is switched andcontrolled so as to selectively input the output of the prefilter 51Awhile reading the preamble P1, the servo mark and address, and the servoburst within the servo region, based on the clock CK1 and the servo markfrom the synchronizing circuit 431, and to selectively input the outputof the prefilter 52A while reading the preamble P2 and the eccentricitycorrection data within the servo region and the preamble P3 and the R/Wdata within the data region, based on the clock CK2 and the servo markfrom the synchronizing circuit 431. In addition, the output of theselector circuit 600 is switched and controlled so as to selectivelyoutput the output of the prefilter part 432 to the servo demodulatingcircuit 436 while reading the servo region, and to selectively outputthe output of the prefilter part 432 to the data demodulating circuit435 while reading the data region, based on the clocks CK1 through CK3and the servo mark from the synchronizing circuit 431.

On the other hand, in the case where the fifth embodiment of theperpendicular magnetic recording medium uses the same format as thethird embodiment, the perpendicular magnetic disk 500-2 has the formatshown in FIG. 10. In this case, the input of the selector circuit 600 isswitched and controlled so as to selectively input the output of theprefilter 51A while reading the preamble P1, the servo mark and address,and the servo burst within the servo region, based on the clock CK1 andthe servo mark from the synchronizing circuit 431, and to selectivelyinput the output of the prefilter 52A while reading the preamble P4, theeccentricity correction data within the servo region and the R/W datawithin the data region, based on the clock CK4 and the servo mark fromthe synchronizing circuit 431. In addition, the output of the selectorcircuit 600 is switched and controlled so as to selectively output theoutput of the prefilter part 432 to the servo demodulating circuit 436while reading the servo region, and to selectively output the output ofthe prefilter part 432 to the data demodulating circuit 435 whilereading the data region, based on the clocks CK1 and CK4 and the servomark from the synchronizing circuit 431.

According to this embodiment, it is possible to obtain effects similarto those obtainable in the first or third embodiment described above.Furthermore, because the selection of the outputs of the prefilters 51Aand 52A within the prefilter part 432 and the selection of thedemodulating circuits 435 and 436 to which the output of the prefilterpart 432 is to be input are made using the single selector circuit 600,it is unnecessary to provide a mechanism for controlling thedemodulating circuits 435 and 436 to the active or inactive states (orto enable or disable the demodulating circuits 435 and 436), it ispossible to simplify the circuit structure.

In each of the embodiments described above, the various timings aregenerated by counting the clock CK1. However, it is of course possibleto generate the various timings by counting clocks other than the clockCK1.

In addition, although the present invention is applied to theperpendicular magnetic disk in the described embodiments, the presentinvention is of course applicable to perpendicular magnetic recordingmedia other than the perpendicular magnetic disk. For example, theperpendicular magnetic recording medium may have a card shape, and thecard-shaped perpendicular magnetic recording medium may have concentrictracks or a spiral track formed thereon.

This application claims the benefit of a Japanese Patent Application No.2006-080580 filed Mar. 23, 2006, in the Japanese Patent Office, thedisclosure of which is hereby incorporated by reference.

Further, the present invention is not limited to these embodiments, butvarious variations and modifications may be made without departing fromthe scope of the present invention.

1. A magnetic storage apparatus comprising: a reproducing headconfigured to reproduce information from a perpendicular magneticrecording medium that is recorded with servo information, eccentricitycorrection data and read/write data; a synchronizing circuit; a filterpart configured to filter a reproduced output of the reproducing head,by filtering the servo information which has a differentiated waveformby a non-differentiating filter characteristic, and by filtering theeccentricity correction data and the read/write data which haverectangular waveforms by a differentiating filter characteristic; ademodulating part configured to demodulate the servo information, theeccentricity correction data and the read/write data that are filteredby the filter part; a servo system configured to carry out a controlprocess including an eccentricity control based on the servo informationand the eccentricity correction data that are demodulated; and a dataprocessing system configured to process the read/write data that aredemodulated; wherein the perpendicular magnetic recording mediumcomprises a servo region and a data region, the servo region is recordedwith a first preamble, the servo information, a second preamble and theeccentricity correction data, and the data region is recorded with athird preamble and the read/write data: the synchronizing circuit isconfigured to generate first through third clocks and a servo mark frompatterns of the first through third preambles having a constant periodand mutually different frequencies, from the reproduced output of thereproducing head, and the filter part is configured to filter thereproduced output by the non-differentiating filter characteristic whilereading the first preamble, the servo mark, and a servo burst within theservo region, based on the first clock and the servo mark, and to filterthe reproduced output by the differentiating filter characteristic whilereading the second preamble and the eccentricity correction data withinthe servo region and the third preamble and the read/write data withinthe data region, based on the second clock and the servo mark.
 2. Themagnetic storage apparatus as claimed in claim 1, wherein thedemodulating part is configured to output the reproduced output that isdemodulated to the servo system while reading the servo region, and tooutput the reproduced output that is demodulated to the data processingsystem while reading the data region, based on the first through thirdclocks and the servo mark.
 3. A signal processing circuit comprising: asynchronizing circuit; a filter part configured to filter a reproducedoutput of a reproducing head, by filtering servo information which has adifferentiated waveform by a non-differentiating filter characteristic,and by filtering an eccentricity correction data and read/write datawhich have rectangular waveforms by a differentiating filtercharacteristic; a demodulating part configured to demodulate the servoinformation, the eccentricity correction data and the read/write datathat are filtered by the filter part; a servo system configured to carryout a control process including an eccentricity control based on theservo information and the eccentricity correction data that aredemodulated; and a data processing system configured to process theread/write data that are demodulated; wherein the reproducing head isconfigured to output the reproduced output by reproducing informationfrom a perpendicular magnetic recording medium comprising a servo regionand a data region, the servo region being recorded with a firstpreamble, the servo information, a second preamble and the eccentricitycorrection data, the data region being recorded with a third preambleand the read/write data, the synchronizing circuit is configured togenerate first through third clocks and a servo mark from patterns ofthe first through third preambles having a constant period and mutuallydifferent frequencies, from the reproduced output of the reproducinghead, and the filter part is configured to filter the reproduced outputby the non-differentiating filter characteristic while reading the firstpreamble, the servo mark, and a servo burst within the servo region,based on the first clock and the servo mark, and to filter thereproduced output by the differentiating filter characteristic whilereading the second preamble and the eccentricity correction data withinthe servo region and the third preamble and the read/write data withinthe data region, based on the second clock and the servo mark.
 4. Thesignal processing circuit as claimed in claim 3, wherein thedemodulating part is configured to output the reproduced output that isdemodulated to the servo system while reading the servo region, and tooutput the reproduced output that is demodulated to the data processingsystem while reading the data region, based on the first through thirdclocks and the servo mark.
 5. A signal processing circuit comprising: asynchronizing circuit; a filter part configured to filter a reproducedoutput of a reproducing head, by filtering servo information which has adifferentiated waveform by a non-differentiating filter characteristic,and by filtering an eccentricity correction data and read/write datawhich have rectangular waveforms by a differentiating filtercharacteristic; a demodulating part configured to demodulate the servoinformation, the eccentricity correction data and the read/write datathat are filtered by the filter part; a servo system configured to carryout a control process including an eccentricity control based on theservo information and the eccentricity correction data that aredemodulated; and a data processing system configured to process theread/write data that are demodulated; wherein the reproducing head isconfigured to output the reproduced output by reproducing informationfrom a perpendicular magnetic recording medium that is recorded withservo information, eccentricity correction data and read/write data, theperpendicular magnetic recording medium comprising a servo region and adata region, the servo region being recorded with a first preamble andthe servo information, the data region being recorded with a secondpreamble, the eccentricity correction data and the read/write data, thesynchronizing circuit is configured to generate first and second clocksand a servo mark from patterns of the first and second preambles havinga constant period and mutually different frequencies, from thereproduced output of the reproducing head, and the filter part isconfigured to filter the reproduced output by the non-differentiatingfilter characteristic while reading the first preamble, the servo mark,and a servo burst within the servo region, based on the first clock andthe servo mark, and to filter the reproduced output by thedifferentiating filter characteristic while reading the second preamble,the eccentricity correction data and the read/write data within the dataregion, based on the second clock and the servo mark.
 6. The signalprocessing circuit as claimed in claim 5, wherein the demodulating partis configured to output the reproduced output that is demodulated to theservo system while reading the servo region, and to output thereproduced output that is demodulated to the data processing systemwhile reading the data region, based on the first through third clocksand the servo mark.
 7. A magnetic storage apparatus comprising: thesignal processing circuit of claim 5; and the reproducing headconfigured to reproduce the information.
 8. The magnetic storageapparatus as claimed in claim 7, wherein the demodulating part isconfigured to output the reproduced output that is demodulated to theservo system while reading the servo region and the eccentricitycorrection data within the data region, and to output the reproducedoutput that is demodulated to the data processing system while readingthe data region, based on the first and second clocks and the servomark.
 9. The magnetic storage apparatus as claimed in claim 7, whereineach information within the servo region comprises a constant frequencyregardless of a region on the perpendicular magnetic recording medium,and each information within the data region comprises a differentfrequency for each region on the perpendicular magnetic recordingmedium.
 10. The magnetic storage apparatus as claimed in claim 7,wherein the demodulating part is configured to output the reproducedoutput that is demodulated to the servo system while reading the servoregion, and to output the reproduced output that is demodulated to thedata processing system while reading the data region, based on the firstthrough third clocks and the servo mark.